WILSON, B.*; MCWILLIAMS, S.: Diet preferences for certain fatty acids and its effect on composition of fat reserves in migratory Red-eyed Vireos
Most birds accumulate large lipid stores as the primary source of energy for fueling their migratory flights. The composition of these lipid stores varies among species; however, 16-carbon and 18-carbon fatty acids typically comprise 50-90% of the lipids. Palmitate (16:0) and oleate (18:1) are usually the predominant fatty acids in the depot fat of migrating birds. We studied fatty acid preferences and the influence of diet on the composition of fat reserves in migratory red-eyed vireos using semi-synthetic diets that differed only in fatty acid composition. Using paired food-preference tests, we found that daily food intake of red-eyed vireos was higher on diets containing triolein (18:1) than diets containing tristearin (18:0), higher on diets containing tripalmitin (16:0) than diets containing tristearin (18:0), and higher on diets containing trimyristin (14:0) than diets containing tripalmitin (16:0). Daily food intake of vireos was similar on diets containing triolein (18:1) and trilinolein (18:2). These results suggest that red-eyed vireos can discriminate between diets differing only in fatty acid composition and that they prefer diets with mostly long-chain unsaturated fatty acids. We studied the effect of fatty acid composition of the diet on the fatty acid composition of fat reserves by maintaining vireos for one month on diets with different dietary fatty acids. The proportion of 16- and 18- carbon fatty acids in the depot fat of vireos was similar to that of their diets. However, the presence of very long-chain unsaturated fatty acids (e.g., 22:4, 24:5) in the depot fat of vireos, despite its absence in the diets, suggests that selective metabolism of fatty acids is also important in determining the fatty acid composition of depot fat in migratory birds.